Earth drilling tools utilize large bits or drill heads formed of solid steel used in a rotative or rotative and percussion action to drill earth and rock and other geological formations.
Percussion drilling is widely used for drilling blast holes in mining and quarrying. Earth boring machines are employed which serve to rotate and reciprocate a percussion tool to which a drill head is attached. For example, a percussion tool may be rotated at about 20 r.p.m., and it may be reciprocated in short strokes of about 4 to 5 inches to produce 500 to 800 impacts per minute. To provide a satisfactory wear life for a drill head, cylindrical recesses are formed in the surface and hard metal inserts are forced into these holes to leave the ends projecting. These inserts, usually formed of tungsten carbide, are supported on the drill head and provide long wearing qualities in comparison to the solid steel heads. Examples of this type of drill head are found in two patents to Frank E. Stebley, U.S. Pat. No. 3,382,940 (May 14, 1968) and U.S. Pat. No. 3,603,414 (Sept. 7, 1971). These patents show drill heads and wear inserts introduced into recesses in the surface. See also the U.S. Pat. to Ott, No. 3,389,761 (June 25, 1968).
In deep earth drilling used in oil well exploration, another use is found for hard metal inserts. Drill pipe may extend into the earth thousands of feet. In most drilling operations, drill string stabilizers are used to prevent excessive wear on the drill pipe and to stabilize the long drill string which is being rotated. These drill stabilizers are generally one piece forgings six to eight inches in diameter and about eighteen inches in length. They are formed with a wide spiral land and groove configuration. The spiral land is provided with multiple radial surface holes into which are introduced tungsten carbide inserts having a protruding nose portion to serve as a wear element to increase the overall life of the stabilizer. These stabilizers are introduced into the drill string at appropriate intervals separated by drill collars and drill pipe. Various spacings will depend on the geological make up of the earth in a particular drilling site.
The present invention relates to the inserts which are utilized in the above-described drilling operations. A cylindrical insert with a serrated side wall has been used as the wear element. This insert is driven into holes in the carrying body in an interference fit and has such a tight fit that air behind the insert is compressed. In order to compensate for this compression, the receiving holes have been drilled twice as deep as the length of the insert. After the carrying body, such as a stabilizer, is worn, the inserts are removed by heating the host body. On occasion the trapped air would expand and project the inserts out like a rifle bullet. This has necessitated the heating in a cage to reduce risk to the operators.
Another problem in connection with these devices has been the difficulty in determining wear on the inserts. It could only be estimated by the time in service or by actual measurement which is time consuming and inconvenient.
It is an object of the invention to provide an improved insert design which eliminates some of the problems inherent in the use of the prior art inserts and which has additional advantages.
It is a specific object to provide an insert which can be driven in to a receiving recess without compressing the air in the recess. Accordingly, the recess can be fitted to the insert and provide a solid bottom support. It is a further object to provide an insert which has a built-in wear indicator which serves not only to indicate wear but also as a relief port when inserts are to be removed by heating the host body. Another optional feature is the provision of a break groove to facilitate insert removal. A benefit of the proposed design lies in an insert with less material, thus an economic savings, and no loss in effective wear characteristics.
Other objects and features of the invention will be apparent in the following description and claims, in which the invention is described together with details directed to persons skilled in the pertinent arts to enable the invention to be practiced in accordance with the disclosure, all in connection with the best mode presently contemplated for the invention.